On Tue, 01 Dec 2009 16:22:08 -0500, Registered User
wrote:

I'm under the impression the current flow
is identical whether metal rods or wire mesh is used in the antenna's
construction.

A discone does not exhibit any quality of shielding, so it wanders off
in that regard.

The difference between rods, number of rods, thickness of rods, and
mesh all speak to bandwidth. 2, 3, or 4 rods will not be remarkable.
16 rods will closely approximate a cone of sheet metal (as would a
grid of similar spacing). The same can be said of the
rod/rods/mesh/sheet in the upper section approximating a solid disk.

Again, all these "appearances" are a strict function of wavelength to
physical length and spacing relationships.

73's
Richard Clark, KB7QHC

On Tue, 01 Dec 2009 16:42:00 -0800, Richard Clark
wrote:

On Tue, 01 Dec 2009 16:22:08 -0500, Registered User
wrote:

I'm under the impression the current flow
is identical whether metal rods or wire mesh is used in the antenna's
construction.

A discone does not exhibit any quality of shielding, so it wanders off
in that regard.


Maybe I'm confused and can't distinguish between Art's all-band mesh
antennas and his mesh Faraday shields.

I was questioning Art's statement
-quote-
When you feed a time varying current to the mesh it is best to view it
in small parts, say a square in the mesh. The hole is a static field
alongside the applied current flows.
- end quote -

The idea of examining the characteristics of a single square of mesh
seems impractical. The impact of adjacent squares should be accounted
for otherwise the single square is a loop.

Either way I've learned as current varies the fields it produces will
vary. If the fields vary they're not static. Too simplistic? What am I
missing?

The difference between rods, number of rods, thickness of rods, and
mesh all speak to bandwidth. 2, 3, or 4 rods will not be remarkable.
16 rods will closely approximate a cone of sheet metal (as would a
grid of similar spacing). The same can be said of the
rod/rods/mesh/sheet in the upper section approximating a solid disk.

IIUC the current flows around the cone of a discone regardless of
solid, sheet or mesh construction. This appears to be contrary to the
quote above where current flows around each individual hole in the
mesh.

Again, all these "appearances" are a strict function of wavelength to
physical length and spacing relationships.


I've built several discones over the years and understand these
relationships. How well is subject to conjecture hi.

On Thu, 03 Dec 2009 16:51:05 -0500, Registered User
wrote:

On Tue, 01 Dec 2009 16:42:00 -0800, Richard Clark
wrote:

On Tue, 01 Dec 2009 16:22:08 -0500, Registered User
wrote:

I'm under the impression the current flow
is identical whether metal rods or wire mesh is used in the antenna's
construction.

A discone does not exhibit any quality of shielding, so it wanders off
in that regard.


Maybe I'm confused and can't distinguish between Art's all-band mesh
antennas and his mesh Faraday shields.

I can understand the confusion. To return to your question above,
there is NOTHING about the discone that falls under the topic of
Faraday shield.

I was questioning Art's statement
-quote-
When you feed a time varying current to the mesh it is best to view it
in small parts, say a square in the mesh. The hole is a static field
alongside the applied current flows.
- end quote -

The idea of examining the characteristics of a single square of mesh
seems impractical. The impact of adjacent squares should be accounted
for otherwise the single square is a loop.

I discussed both the single mesh opening, and the total contribution
of all mesh openings. To respond to your last statement, yes, the
single square is a loop. A very, very inefficient coupler of energy.

Either way I've learned as current varies the fields it produces will
vary. If the fields vary they're not static. Too simplistic? What am I
missing?

Static comes in two flavors. One means "not moving." The other means
high potential (which can be "not moving" AND, ironically, "moving").
Such is the legacy of electrostatic potential covering DC to Gamma.

The difference between rods, number of rods, thickness of rods, and
mesh all speak to bandwidth. 2, 3, or 4 rods will not be remarkable.
16 rods will closely approximate a cone of sheet metal (as would a
grid of similar spacing). The same can be said of the
rod/rods/mesh/sheet in the upper section approximating a solid disk.

IIUC the current flows around the cone of a discone regardless of
solid, sheet or mesh construction. This appears to be contrary to the
quote above where current flows around each individual hole in the
mesh.

Well, language can be a barrier here when you say "around the cone."

Go to:
http://www.antenna-theory.com/antenn...rture/slot.php
I don't endorse this page, but it gives you a beginning for slot
antennas and especially the construction mimicry between them and a
dipole. Note in figure two that a "source" appears across the two. In
the case of the slot antenna, this source would give rise to a
circulating current. If you were to approach this with knowing the
current alone, it would follow that the source is "apparent." In
other words, the two models (or experiences) are equivalent.

Do not confuse this circulating current with a larger, general current
UNLESS that more general one can spawn the circulating one. I wrote
to this already and to put it shortly, it is physical length vs. wave
length dependant.

Again, all these "appearances" are a strict function of wavelength to
physical length and spacing relationships.


I've built several discones over the years and understand these
relationships. How well is subject to conjecture hi.

http://www.qsl.net/kb7qhc/antenna/Discone/discone.htm
will illustrate how varying the flare of the skirt shifts the
operating properties of the discone.

73's
Richard Clark, KB7QHC

On Thu, 03 Dec 2009 14:13:57 -0800, Richard Clark
wrote:

On Thu, 03 Dec 2009 16:51:05 -0500, Registered User
wrote:

- good stuff from RC snipped -

Either way I've learned as current varies the fields it produces will
vary. If the fields vary they're not static. Too simplistic? What am I
missing?

Static comes in two flavors. One means "not moving." The other means
high potential (which can be "not moving" AND, ironically, "moving").
Such is the legacy of electrostatic potential covering DC to Gamma.

I was wondering about the latter as a possibility but couldn't find
the proper words. My interpretation is although the individual fields
may vary the total potential of the fields is constant. Is this
correct?

The difference between rods, number of rods, thickness of rods, and
mesh all speak to bandwidth. 2, 3, or 4 rods will not be remarkable.
16 rods will closely approximate a cone of sheet metal (as would a
grid of similar spacing). The same can be said of the
rod/rods/mesh/sheet in the upper section approximating a solid disk.

IIUC the current flows around the cone of a discone regardless of
solid, sheet or mesh construction. This appears to be contrary to the
quote above where current flows around each individual hole in the
mesh.

Well, language can be a barrier here when you say "around the cone."

I should have said the current flows around the cone parallel to its
base.

- more snippage -

I appreciate the clarifications and the links. It all helps to better
my knowledge and understanding of these topics. Thank you

On Fri, 04 Dec 2009 07:04:28 -0500, Registered User
wrote:

Static comes in two flavors. One means "not moving." The other means
high potential (which can be "not moving" AND, ironically, "moving").
Such is the legacy of electrostatic potential covering DC to Gamma.

I was wondering about the latter as a possibility but couldn't find
the proper words. My interpretation is although the individual fields
may vary the total potential of the fields is constant. Is this
correct?

Electrostatic is properly applied to charge that is NOT moving, or
moving very slowly.

The same thing can be said of Magnetostatics as being derived from a
current that is constant, or altering very slowly.

The sense of either of these strict terms residing in the RF denotes
the poverty of idea that takes up residence here as invention. There
is plenty of examples to be found on the Web too. It is unfortunate,
like the camel's nose under the Arab's tent, that taking "very slowly"
and winding out the tach to 100GHz is the pollution of meaning.

What we are concerned here with is electromagnetics infrequently known
as electrodynamics and rarely as magnetodynamics. The sense behind
electromagnetics is inclusive of dynamics of which statics is a
special case.

Dynamics, of course, means time-varying. In EMF, or electromagnetics,
what varies is magnitude and/or polarity of the electric and magnetic
field. What you find "constant" about the fields (properly observed
as plural) is in their orthogonality (one field is building the other
as it decays in amplitude).

Well, language can be a barrier here when you say "around the cone."

I should have said the current flows around the cone parallel to its
base.

That doesn't happen.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote
...
On Fri, 04 Dec 2009 07:04:28 -0500, Registered User
wrote:

Static comes in two flavors. One means "not moving." The other means
high potential (which can be "not moving" AND, ironically, "moving").
Such is the legacy of electrostatic potential covering DC to Gamma.

I was wondering about the latter as a possibility but couldn't find
the proper words. My interpretation is although the individual fields
may vary the total potential of the fields is constant. Is this
correct?

Electrostatic is properly applied to charge that is NOT moving, or
moving very slowly.

The same thing can be said of Magnetostatics as being derived from a
current that is constant, or altering very slowly.

The sense of either of these strict terms residing in the RF denotes
the poverty of idea that takes up residence here as invention. There
is plenty of examples to be found on the Web too. It is unfortunate,
like the camel's nose under the Arab's tent, that taking "very slowly"
and winding out the tach to 100GHz is the pollution of meaning.

What we are concerned here with is electromagnetics infrequently known
as electrodynamics and rarely as magnetodynamics. The sense behind
electromagnetics is inclusive of dynamics of which statics is a
special case.

Between statics and dynamics is kinetics. EM is the kinetics.
S*

Dynamics, of course, means time-varying. In EMF, or electromagnetics,
what varies is magnitude and/or polarity of the electric and magnetic
field. What you find "constant" about the fields (properly observed
as plural) is in their orthogonality (one field is building the other
as it decays in amplitude).

Well, language can be a barrier here when you say "around the cone."

I should have said the current flows around the cone parallel to its
base.

That doesn't happen.

73's
Richard Clark, KB7QHC

"Szczepan Bialek" wrote in
:

Between statics and dynamics is kinetics. EM is the kinetics.


This could either get very confusing, or very revealing, not sure which yet.
I found that no terms I knew fitted that well so I ended up using 'flux' and
'stasis' NOT to be confused with motion and stillness. By which I mean motion
and stillness are the phenomenon, but flux and stasis are what lies beyond,
in a pattern of information for want of better expression. To illustrate, a
tap turned to release a flow of water often shows a stationary pattern while
water is obviously flowing. That pattern is a stasis, but the water is not
still. I don't know how useful this is when resolving a distinction between
kinetics and dynamics, but it does look like we have to be careful about how
we use these terms or we might not know which we're talking about, the
standing pattern, or a manifest stillness. If we can't be clear on it we
might as well be trying to pin down the 'evanescence of soul'. (Richard
Clark, that was a good one, it's right up there with the better phrases from
Douglas Adams.)